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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |ATTRIBUTES |STANDARDS |HISTORY |NOTES |BUGS |EXAMPLES |SEE ALSO |COLOPHON | |
getrlimit(2) System Calls Manualgetrlimit(2)getrlimit, setrlimit, prlimit - get/set resource limits
Standard C library (libc,-lc)
#include <sys/resource.h>int getrlimit(intresource, struct rlimit *rlim);int setrlimit(intresource, const struct rlimit *rlim);int prlimit(pid_tpid, intresource,const struct rlimit *_Nullablenew_limit,struct rlimit *_Nullableold_limit);struct rlimit {rlim_t rlim_cur;/* Soft limit */rlim_t rlim_max;/* Hard limit (ceiling for rlim_cur) */};typedef/* ... */rlim_t;/* Unsigned integer type */ Feature Test Macro Requirements for glibc (seefeature_test_macros(7)):prlimit(): _GNU_SOURCEThegetrlimit() andsetrlimit() system calls get and set resource limits. Each resource has an associated soft and hard limit, as defined by therlimit structure. The soft limit is the value that the kernel enforces for the corresponding resource. The hard limit acts as a ceiling for the soft limit: an unprivileged process may set only its soft limit to a value in the range from 0 up to the hard limit, and (irreversibly) lower its hard limit. A privileged process (under Linux: one with theCAP_SYS_RESOURCEcapability in the initial user namespace) may make arbitrary changes to either limit value. The valueRLIM_INFINITYdenotes no limit on a resource (both in the structure returned bygetrlimit() and in the structure passed tosetrlimit()). Theresource argument must be one of:RLIMIT_AS This is the maximum size of the process's virtual memory (address space). The limit is specified in bytes, and is rounded down to the system page size. This limit affects calls tobrk(2),mmap(2), andmremap(2), which fail with the errorENOMEMupon exceeding this limit. In addition, automatic stack expansion fails (and generates aSIGSEGV that kills the process if no alternate stack has been made available viasigaltstack(2)). Since the value is along, on machines with a 32-bitlong either this limit is at most 2 GiB, or this resource is unlimited.RLIMIT_CORE This is the maximum size of acore file (seecore(5)) in bytes that the process may dump. When 0 no core dump files are created. When nonzero, larger dumps are truncated to this size.RLIMIT_CPU This is a limit, in seconds, on the amount of CPU time that the process can consume. When the process reaches the soft limit, it is sent aSIGXCPUsignal. The default action for this signal is to terminate the process. However, the signal can be caught, and the handler can return control to the main program. If the process continues to consume CPU time, it will be sentSIGXCPUonce per second until the hard limit is reached, at which time it is sentSIGKILL. (This latter point describes Linux behavior. Implementations vary in how they treat processes which continue to consume CPU time after reaching the soft limit. Portable applications that need to catch this signal should perform an orderly termination upon first receipt ofSIGXCPU.)RLIMIT_DATA This is the maximum size of the process's data segment (initialized data, uninitialized data, and heap). The limit is specified in bytes, and is rounded down to the system page size. This limit affects calls tobrk(2),sbrk(2), and (since Linux 4.7)mmap(2), which fail with the errorENOMEMupon encountering the soft limit of this resource.RLIMIT_FSIZE This is the maximum size in bytes of files that the process may create. Attempts to extend a file beyond this limit result in delivery of aSIGXFSZsignal. By default, this signal terminates a process, but a process can catch this signal instead, in which case the relevant system call (e.g.,write(2),truncate(2)) fails with the errorEFBIG.RLIMIT_LOCKS(Linux 2.4.0 to Linux 2.4.24) This is a limit on the combined number offlock(2) locks andfcntl(2) leases that this process may establish.RLIMIT_MEMLOCK This is the maximum number of bytes of memory that may be locked into RAM. This limit is in effect rounded down to the nearest multiple of the system page size. This limit affectsmlock(2),mlockall(2), and themmap(2)MAP_LOCKED operation. Since Linux 2.6.9, it also affects theshmctl(2)SHM_LOCKoperation, where it sets a maximum on the total bytes in shared memory segments (seeshmget(2)) that may be locked by the real user ID of the calling process. Theshmctl(2)SHM_LOCKlocks are accounted for separately from the per-process memory locks established bymlock(2),mlockall(2), andmmap(2)MAP_LOCKED; a process can lock bytes up to this limit in each of these two categories. Before Linux 2.6.9, this limit controlled the amount of memory that could be locked by a privileged process. Since Linux 2.6.9, no limits are placed on the amount of memory that a privileged process may lock, and this limit instead governs the amount of memory that an unprivileged process may lock.RLIMIT_MSGQUEUE(since Linux 2.6.8) This is a limit on the number of bytes that can be allocated for POSIX message queues for the real user ID of the calling process. This limit is enforced formq_open(3). Each message queue that the user creates counts (until it is removed) against this limit according to the formula: Since Linux 3.5: bytes = attr.mq_maxmsg * sizeof(struct msg_msg) + MIN(attr.mq_maxmsg, MQ_PRIO_MAX) * sizeof(struct posix_msg_tree_node)+ /* For overhead */ attr.mq_maxmsg * attr.mq_msgsize; /* For message data */ Linux 3.4 and earlier: bytes = attr.mq_maxmsg * sizeof(struct msg_msg *) + /* For overhead */ attr.mq_maxmsg * attr.mq_msgsize; /* For message data */ whereattr is themq_attr structure specified as the fourth argument tomq_open(3), and themsg_msg andposix_msg_tree_node structures are kernel-internal structures. The "overhead" addend in the formula accounts for overhead bytes required by the implementation and ensures that the user cannot create an unlimited number of zero-length messages (such messages nevertheless each consume some system memory for bookkeeping overhead).RLIMIT_NICE(since Linux 2.6.12, but see BUGS below) This specifies a ceiling to which the process's nice value can be raised usingsetpriority(2) ornice(2). The actual ceiling for the nice value is calculated as20 - rlim_cur. The useful range for this limit is thus from 1 (corresponding to a nice value of 19) to 40 (corresponding to a nice value of -20). This unusual choice of range was necessary because negative numbers cannot be specified as resource limit values, since they typically have special meanings. For example,RLIM_INFINITYtypically is the same as -1. For more detail on the nice value, seesched(7).RLIMIT_NOFILE This specifies a value one greater than the maximum file descriptor number that can be opened by this process. Attempts (open(2),pipe(2),dup(2), etc.) to exceed this limit yield the errorEMFILE. (Historically, this limit was namedRLIMIT_OFILEon BSD.) Since Linux 4.5, this limit also defines the maximum number of file descriptors that an unprivileged process (one without theCAP_SYS_RESOURCEcapability) may have "in flight" to other processes, by being passed across UNIX domain sockets. This limit applies to thesendmsg(2) system call. For further details, seeunix(7).RLIMIT_NPROC This is a limit on the number of extant process (or, more precisely on Linux, threads) for the real user ID of the calling process. So long as the current number of processes belonging to this process's real user ID is greater than or equal to this limit,fork(2) fails with the errorEAGAIN. TheRLIMIT_NPROClimit is not enforced for processes that have either theCAP_SYS_ADMINor theCAP_SYS_RESOURCE capability, or run with real user ID 0.RLIMIT_RSS This is a limit (in bytes) on the process's resident set (the number of virtual pages resident in RAM). This limit has effect only in Linux 2.4.x, x < 30, and there affects only calls tomadvise(2) specifyingMADV_WILLNEED.RLIMIT_RTPRIO(since Linux 2.6.12, but see BUGS) This specifies a ceiling on the real-time priority that may be set for this process usingsched_setscheduler(2) andsched_setparam(2). For further details on real-time scheduling policies, seesched(7)RLIMIT_RTTIME(since Linux 2.6.25) This is a limit (in microseconds) on the amount of CPU time that a process scheduled under a real-time scheduling policy may consume without making a blocking system call. For the purpose of this limit, each time a process makes a blocking system call, the count of its consumed CPU time is reset to zero. The CPU time count is not reset if the process continues trying to use the CPU but is preempted, its time slice expires, or it callssched_yield(2). Upon reaching the soft limit, the process is sent aSIGXCPU signal. If the process catches or ignores this signal and continues consuming CPU time, thenSIGXCPUwill be generated once each second until the hard limit is reached, at which point the process is sent aSIGKILLsignal. The intended use of this limit is to stop a runaway real- time process from locking up the system. For further details on real-time scheduling policies, seesched(7)RLIMIT_SIGPENDING(since Linux 2.6.8) This is a limit on the number of signals that may be queued for the real user ID of the calling process. Both standard and real-time signals are counted for the purpose of checking this limit. However, the limit is enforced only forsigqueue(3); it is always possible to usekill(2) to queue one instance of any of the signals that are not already queued to the process.RLIMIT_STACK This is the maximum size of the process stack, in bytes. Upon reaching this limit, aSIGSEGVsignal is generated. To handle this signal, a process must employ an alternate signal stack (sigaltstack(2)). Since Linux 2.6.23, this limit also determines the amount of space used for the process's command-line arguments and environment variables; for details, seeexecve(2).prlimit() The Linux-specificprlimit() system call combines and extends the functionality ofsetrlimit() andgetrlimit(). It can be used to both set and get the resource limits of an arbitrary process. Theresource argument has the same meaning as forsetrlimit() andgetrlimit(). If thenew_limit argument is not NULL, then therlimit structure to which it points is used to set new values for the soft and hard limits forresource. If theold_limit argument is not NULL, then a successful call toprlimit() places the previous soft and hard limits forresource in therlimit structure pointed to byold_limit. Thepid argument specifies the ID of the process on which the call is to operate. Ifpid is 0, then the call applies to the calling process. To set or get the resources of a process other than itself, the caller must have theCAP_SYS_RESOURCEcapability in the user namespace of the process whose resource limits are being changed, or the real, effective, and saved set user IDs of the target process must match the real user ID of the callerand the real, effective, and saved set group IDs of the target process must match the real group ID of the caller.
On success, these system calls return 0. On error, -1 is returned, anderrno is set to indicate the error.
EFAULTA pointer argument points to a location outside the accessible address space.EINVALThe value specified inresource is not valid; or, forsetrlimit() orprlimit():rlim->rlim_cur was greater thanrlim->rlim_max.EPERMAn unprivileged process tried to raise the hard limit; theCAP_SYS_RESOURCEcapability is required to do this.EPERMThe caller tried to increase the hardRLIMIT_NOFILElimit above the maximum defined by/proc/sys/fs/nr_open (seeproc(5))EPERM(prlimit()) The calling process did not have permission to set limits for the process specified bypid.ESRCHCould not find a process with the ID specified inpid.
For an explanation of the terms used in this section, seeattributes(7). ┌──────────────────────────────────────┬───────────────┬─────────┐ │Interface│Attribute│Value│ ├──────────────────────────────────────┼───────────────┼─────────┤ │getrlimit(),setrlimit(),prlimit() │ Thread safety │ MT-Safe │ └──────────────────────────────────────┴───────────────┴─────────┘
getrlimit()setrlimit() POSIX.1-2008.prlimit() Linux.RLIMIT_MEMLOCKandRLIMIT_NPROCderive from BSD and are not specified in POSIX.1; they are present on the BSDs and Linux, but on few other implementations.RLIMIT_RSSderives from BSD and is not specified in POSIX.1; it is nevertheless present on most implementations.RLIMIT_MSGQUEUE,RLIMIT_NICE,RLIMIT_RTPRIO,RLIMIT_RTTIME, andRLIMIT_SIGPENDINGare Linux-specific.
getrlimit()setrlimit() POSIX.1-2001, SVr4, 4.3BSD.prlimit() Linux 2.6.36, glibc 2.13.
A child process created viafork(2) inherits its parent's resource limits. Resource limits are preserved acrossexecve(2). Resource limits are per-process attributes that are shared by all of the threads in a process. Lowering the soft limit for a resource below the process's current consumption of that resource will succeed (but will prevent the process from further increasing its consumption of the resource). One can set the resource limits of the shell using the built-inulimit command (limit incsh(1)). The shell's resource limits are inherited by the processes that it creates to execute commands. Since Linux 2.6.24, the resource limits of any process can be inspected via/proc/pid/limits; seeproc(5). Ancient systems provided avlimit() function with a similar purpose tosetrlimit(). For backward compatibility, glibc also providesvlimit(). All new applications should be written usingsetrlimit().C library/kernel ABI differences Since glibc 2.13, the glibcgetrlimit() andsetrlimit() wrapper functions no longer invoke the corresponding system calls, but instead employprlimit(), for the reasons described in BUGS. The name of the glibc wrapper function isprlimit(); the underlying system call isprlimit64().
In older Linux kernels, theSIGXCPUandSIGKILLsignals delivered when a process encountered the soft and hardRLIMIT_CPUlimits were delivered one (CPU) second later than they should have been. This was fixed in Linux 2.6.8. In Linux 2.6.x kernels before Linux 2.6.17, aRLIMIT_CPUlimit of 0 is wrongly treated as "no limit" (likeRLIM_INFINITY). Since Linux 2.6.17, setting a limit of 0 does have an effect, but is actually treated as a limit of 1 second. A kernel bug means thatRLIMIT_RTPRIOdoes not work in Linux 2.6.12; the problem is fixed in Linux 2.6.13. In Linux 2.6.12, there was an off-by-one mismatch between the priority ranges returned bygetpriority(2) andRLIMIT_NICE. This had the effect that the actual ceiling for the nice value was calculated as19 - rlim_cur. This was fixed in Linux 2.6.13. Since Linux 2.6.12, if a process reaches its softRLIMIT_CPUlimit and has a handler installed forSIGXCPU, then, in addition to invoking the signal handler, the kernel increases the soft limit by one second. This behavior repeats if the process continues to consume CPU time, until the hard limit is reached, at which point the process is killed. Other implementations do not change theRLIMIT_CPUsoft limit in this manner, and the Linux behavior is probably not standards conformant; portable applications should avoid relying on this Linux-specific behavior. The Linux-specificRLIMIT_RTTIMElimit exhibits the same behavior when the soft limit is encountered. Kernels before Linux 2.4.22 did not diagnose the errorEINVALforsetrlimit() whenrlim->rlim_cur was greater thanrlim->rlim_max. Linux doesn't return an error when an attempt to setRLIMIT_CPU has failed, for compatibility reasons.Representation of "large" resource limit values on 32-bit platforms The glibcgetrlimit() andsetrlimit() wrapper functions use a 64-bitrlim_t data type, even on 32-bit platforms. However, therlim_t data type used in thegetrlimit() andsetrlimit() system calls is a (32-bit)unsigned long. Furthermore, in Linux, the kernel represents resource limits on 32-bit platforms asunsignedlong. However, a 32-bit data type is not wide enough. The most pertinent limit here isRLIMIT_FSIZE, which specifies the maximum size to which a file can grow: to be useful, this limit must be represented using a type that is as wide as the type used to represent file offsets—that is, as wide as a 64-bitoff_t (assuming a program compiled with_FILE_OFFSET_BITS=64). To work around this kernel limitation, if a program tried to set a resource limit to a value larger than can be represented in a 32-bitunsigned long, then the glibcsetrlimit() wrapper function silently converted the limit value toRLIM_INFINITY. In other words, the requested resource limit setting was silently ignored. Since glibc 2.13, glibc works around the limitations of thegetrlimit() andsetrlimit() system calls by implementingsetrlimit() andgetrlimit() as wrapper functions that callprlimit().
The program below demonstrates the use ofprlimit(). #define _GNU_SOURCE #define _FILE_OFFSET_BITS 64 #include <err.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> #include <sys/resource.h> #include <time.h> int main(int argc, char *argv[]) { pid_t pid; struct rlimit old, new; struct rlimit *newp; if (!(argc == 2 || argc == 4)) { fprintf(stderr, "Usage: %s <pid> [<new-soft-limit> " "<new-hard-limit>]\n", argv[0]); exit(EXIT_FAILURE); } pid = atoi(argv[1]); /* PID of target process */ newp = NULL; if (argc == 4) { new.rlim_cur = atoi(argv[2]); new.rlim_max = atoi(argv[3]); newp = &new; } /* Set CPU time limit of target process; retrieve and display previous limit */ if (prlimit(pid, RLIMIT_CPU, newp, &old) == -1) err(EXIT_FAILURE, "prlimit-1"); printf("Previous limits: soft=%jd; hard=%jd\n", (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max); /* Retrieve and display new CPU time limit */ if (prlimit(pid, RLIMIT_CPU, NULL, &old) == -1) err(EXIT_FAILURE, "prlimit-2"); printf("New limits: soft=%jd; hard=%jd\n", (intmax_t) old.rlim_cur, (intmax_t) old.rlim_max); exit(EXIT_SUCCESS); }prlimit(1),dup(2),fcntl(2),fork(2),getrusage(2),mlock(2),mmap(2),open(2),quotactl(2),sbrk(2),shmctl(2),malloc(3),sigqueue(3),ulimit(3),core(5),capabilities(7),cgroups(7),credentials(7),signal(7)
This page is part of theman-pages (Linux kernel and C library user-space interface documentation) project. Information about the project can be found at ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report for this manual page, see ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩. This page was obtained from the tarball man-pages-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. If you discover any rendering problems in this HTML version of the page, or you believe there is a better or more up- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17getrlimit(2)Pages that refer to this page:homectl(1), prlimit(1), renice(1), strace(1), systemd-nspawn(1), brk(2), dup(2), execve(2), F_DUPFD(2const), F_GETSIG(2const), fork(2), getpriority(2), getrusage(2), io_uring_register(2), io_uring_setup(2), madvise(2), memfd_secret(2), mlock(2), mmap(2), mremap(2), nice(2), open(2), perf_event_open(2), pidfd_getfd(2), pidfd_open(2), PR_SET_MM_START_BRK(2const), quotactl(2), seccomp(2), seccomp_unotify(2), select(2), shmctl(2), sigaltstack(2), syscalls(2), timer_create(2), write(2), errno(3), getdtablesize(3), io_uring_register_files(3), io_uring_register_files_sparse(3), io_uring_register_files_tags(3), io_uring_register_files_update(3), io_uring_register_files_update_tag(3), malloc(3), mq_open(3), pthread_attr_setstacksize(3), pthread_create(3), pthread_getattr_np(3), pthread_setschedparam(3), pthread_setschedprio(3), ulimit(3), core(5), limits.conf(5), lxc.container.conf(5), proc_pid_limits(5), proc_pid_stat(5), proc_pid_status(5), proc_sys_fs(5), proc_sys_kernel(5), systemd.exec(5), systemd-system.conf(5), capabilities(7), cgroups(7), credentials(7), fanotify(7), mq_overview(7), pthreads(7), sched(7), signal(7), time(7), unix(7), systemd-coredump(8)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |